Protective means for fan cooled rectifiers and the like



E. A. HARTY July 26, 1938..

PROTECTIVE MEANS FOR FAN COOLED RECTIFIERS AND THE LIKE Filed March 10, 1956 5 Sheets-Sheet 1 Fig.1.

Irwverwtor Edgar Afiartg, 10 3 4/14 6, JMLM 3 His Attorne g.

July 26, 1938.

E. A. HARTY 2,125,110 PROTECTIVE MEANS FOR FAN COOLED RECTIFIERS AND THE LIKE Filed March 10, 1956 3 Sheets-Sheet 2 l A l -37 EdgarAJ-iartg,

July 26, 1938. HARTY 2,125,119

PROTECTIVE MEANS FOR FAN COOLED RECTIFIERS AND THE LIKE Filed March 10, 1936 3 Sheets-Sheet 3 lrwvemtori' EdgahAfiartg HisAttorrweg.

Patented July 26, 1938 PATENT OFFICE RECTIFIERS AND PROTECTIVE MEANS FOR FAN COOLED THE LIKE Edgar A. Barty, Marbiehcad, Masa, assignmto General Electric Company, a corporation of New York Application March 1c, 1936, Serial No. 88,061 11 Claims. (or 111-314) My invention relates to apparatus which requires in its operation a current of cooling medium to remove heat losses and which is subject to damage due to overheating in the event of the stoppage of the current of cooling medium.

{lhe invention relates more particularly to rectifier apparatus including rectifier devices of the contact type arranged for relatively large power output and in which a rise in operating temperalc ture above a predetermined safe limit is prevented by a blower means.

Rectifying apparatus is commonly employed to supply direct current from alternating current power lines for are lamps of motion picture pro- "ld jectors and for charging storage batteries. For

these and similar uses fan cooled contact rectifiers of the copper oxide type, as described for example in Amsden Patent 1,947,240, assigned to the same assignee as the present application, are

eminently suitable by reason of their simplicit compactness, reliability in operation, and long life.

The copper oxide rectifier, however, is a device which is injured if the temperature therein is 5 permitted to rise more than a predetermined number of degrees, and dimcultles have been encountered in the use of apparatus employing contact rectifier devices due to the disablement or stoppage of the blower means supplying the cool- 30 log air for the rectifier devices with consequent destructive rise or" the rectifier temperature.

It has been proposed heretofore to protect rectifiers and like devices from injury due to overheating upon stoppage of the blower means by 35 the provision, for example, of usual thermostatic protective devices designed to be operated di= rectly in response to the temperature rise in the rectifier device, but such means has not proved in practice efiective to forestall without fail dan- 40 gerous overheating suficient at times to destroy the rectifier unit, which then requires replacement at considerable cost.

In other types of apparatus also, such as electric current transformers, wherein operating con- 45 ditions and requirements have been such that a dangerous or destructive overheating of the apparatus resulted upon disablement or stoppage of the air blast or other current of cooling medium, the provision of the usual thermostatic 50 protective means responsive only to the dangerous rise in temperature of the apparatus itself has in certain cases proved inadequate.

It is an object of my invention to prevent dam age from overheating in apparatus cooled by a 55 current of cooling medium to remove the heat losses, by protective means responsive directly to the current of cooling medium, whereby during normal operation of the cooling device the operation of the apparatus is permitted to continue, but upon occurrence of impairment or stoppage 5 of the cooling current the development of heat losses is stopped or the operation of the apparatus is discontinued.

A further object is to prevent damage from overheating in apparatus cooled by a blower it means providing an air blast, by protective means arranged to operate in response to the air blast.

A particular object is to prevent overheating or a rectifier device cooled by an air blast, by

thermostatic switch means arranged to operate 5 in response to the air blast.

Another object is to prevent overheating of a blower cooled rectifier apparatus for supplying direct current to a load such as a motion picture are from an alternating current circuit, by means 29 including a control circuit and a thermostatic means energized from the control circuit and arranged to control the operation of the rectifier apparatus in response to the air blast from the blower.

A further object is to prevent overheating or? a blower cooled rectifier apparatus for su plying charging current to a storage battery from an alternating current circuit, to prevent operation of the rectifier unless the storage batteries are 30 connected for charging, and to prevent the rectifier from being connected to the battery in case the alternating current circuit falls, by means including a thermostatic switch means operating in response to the air blast from the blower.

A further object is to prevent overheating of a blower cooled transformer apparatus, by means including a thermostatic switch means operating in response to an air blast from the blower.

In accordance with my invention the foregoing objects, and other objects and advantages which will hereinafter appear, are obtained by the provision, in the rectifier or other apparatus subject to overheating upon disablement of a blower or other means for supplying a current of cooling medium, of a protective means normally continuously so energized that the operation of the rectifier or other apparatus would be prevented by the action of the protective means if the functioning thereof were not blocked by the action of the current of cooling medium on the protective means. Upon disablement of the cooling medium supply means, accompanied by reduced flow or entire stoppage of flow of the cooling medium, the blocking efiect of the current flow on the protective means is prevented operation of the rectifier apparatus. v

page of,the air blast for any reason, or reduction,

and the protective means then functions to stop the heat-losses in the apparatusor to stop the operation of the apparatus.

of the air blast below a predetermined limit, the cooling effect bf the air blast disappears or diminishes thereby; permitting the temperature -of the continually-energized heatable element to rise sumciently to cause the thermostatic means to function as a control means to cut the rectiiler apparatus from the supply circuit or other-v wise to prevent damage due to overheating of the apparatus.

Further, in accordance with my invention, in case the invention is applied to rectifying systems for charging storage batteries, a means-is provided, operating independently of or in con- Junction with the above-mentioned thermostatic means and associated preferably with the charging terminals through which the battery is connected to the rectifier apparatus, for preventing the connection of the alternating current supply circuit to the'rectifier unless the storage battery is firstconnectedto the rectifier circuit.

My invention will be better understood from the following description when considered in 0011-. nection with the accompanying drawings, and its scope will be set forth in the appended claims.

Referring to the drawings, Fig. 1 is a diagrammatic representation of a rectifier system for supplying direct current to a motion picture are or like load from an alternating current circuit, in

which my invention has been embodied; Figs. 2 and 3 are respectively a plan View and a side-elevational view of a thermostatic device which may be utilized in carrying the invention into efiect; Figs. 4 and 5 are respectively a plan view'and a 'side-elevational view of another thermostatic device which may be utilized in carrying the inven tion into effect; Figs. 6 and 7 are diagrammatic representations of rectifying systems for supplying charging current to a storage battery from an alternating current circuit, in which my invention has been embodied; Fig. 8 illustrates a rectifying system similar to that of Fig. 1 but arranged to supply current for charging storage batteries; and Fig. 9 illustrates diagrammatically an electric transformer system in which my invention has been embodied.

In Fig. 1, the numeral ill designates a direct current circuit which may be connected to supply current to a motion picture are or like load '(not shown) from a three-phase alternating current circuit ll through a transformer l2 and a rectifying apparatus it including a plurality of contact rectifier devices It, preferably of the copper oxide type, and a blower means or fan It to direct an air blast on the rectifiers. -'I'he fan l5 is driven by a motor it connected directly through a line switch I? to a'control circuit is which, in case the rectifier apparatus is used to supply a motion picture are, may be conveniently the alternating current sound system circuit. To connect the rectifier apparatus l3 through transformer IE to the alternating current circuit H, a switch means i9 is provided, in two of the phases of cir-' mounted in the blowerair blast cult II, having operating windings 20 energized from the control circuit it through switch ii to close the contacts 2| of the switch means l9:

To provide means for disconnectingthe rectifier apparatus it from the supply circuit H in 5 the event ofdisablement pf the blower means, the operating windings 28 of switch means it are "connectedto control circuit it through normally closed contacts 22, 23 of a thermostatic switch means of unit 2% having a heater means 25 a1'- 10 ranged to heat one of the elements as 26 of the contact carrying elements 26, 2?. The heater 25 is arranged to be'continually energized from control circuit it but is continually cooled during normal operation of the rectifier system, since the thermostatic-switch unit 26 is so mounted as to be exposed to an air blast due to fan It.

In the operation of the rectified system illuse trated in Fig. 1, the switch means l9 and the thermostatic switch unit 23 being in their illus- 2o trated positions, upon closing of switch I? contacts 2| of switch l9 areclosed by current from control circuit l8 flowing in the operating wind lugs through contacts 22, 23, and motor it is started by current from circuit iii to drive 25 fan l5. Heater element 25 is at the time energized by current from circuit l8 and begins immediately to heat, thereby tending to transmit to the adjacent thermostatic switch element 26 sufficient heat to cause the latter to operate so the contacts 22, 23 and thereby to deenergize re- -laywindings 20 to operate contacts 2i of the alternating current line switch l9. But, since the fan i5 is now rotating, the air blast produced thereby prevents the thermostatic switch unit 2Q. from functioning, due to the cooling efiect of the air blast on heater 25 and on the thermostatic switch blades. However, if upon closing ofthe switch l'l to connect the supply circuit H to the g fan motor l6 and to the rectifier apparatus as an above described, the fan l5 does not start to rotate within a predetermined time limit, for example from 1 to 2 minutes, the thermostatic switch unit 26 becomes heated sufiiciently to open the contacts 22, 23 thereby. disconnecting'coils 29 from the circuit it which supplies these actuating coils of the line switch l9 causing the latter. switch l9 to trip and to disconnect the alternating current supply line H from the rectifier apparatus. Further, if at any time during normal "operation of the rectifier system. the "air blast from fan 15 fails or is reduced below a predetermined limit, from mechanical iamming of the fan, open circuiting or short-circuiting of the motor l6, failure of the control circuit H3; or from any cause whatsoever, the protective means ineluding thermostatic switch unit 26 will function. as above described to protect the rectifier devices Hi from overheating.

The thermostatic switch unit illustrated in Figs. 2 and 3 assuitable for the purposes of my invention comprises two coacting bimetallic thermostatic elements 28, 29 carrying coacting contacts 30, 3i at their free ends and mounted upon opposite sides of a supporting and insulating plate 32 upon which is mounted a heater element 33 closely adjacent the corresponding bimetallic thermostatic element 28 but separated'from the other element, 29, by the plate. In Figs. 4 and 5 the thermostatic switch unit comprises two like metal elements or strips 34, 35 mounted on opposite sides of an insulating base plate 36and rigidly connected at their free ends by a bar or post 37. A heater. element 38 is mounted on the 35, but is separated by the plate from the other metal strip 34 which carries a contact 39 coacting with a fixed contact 40 mounted on the base 36. In operation of the thermostatic unit shown in ,Figs'n2 and 3 it will be understood that the device is of the type compensated for ambient temperature since the bimetallic elements 28 and 29 move simultaneously in the same direction under the influence of ambient temperature variation, and that upon suificient heating of the element 28 by heater 33 the element 28 bends to open the contacts 36, Si. It will also be understood that the'thermostatic switch element or unit shown in Figs. and 5 is also compensated for ambient temperature variations since the like strips t l, 35 expand equally for agiven temperature change, and that upon heating of strip 35 by heater 3d the strip 35 expands more than the other strip 3 3 causing the latter to bend and to open the contacts 3%, Qt.

In Fig. 6, the numeral ii designates a direct current circuit adapted to be connected to a pair of cables 52, 63 for charging a storage battery (not shown) from the three-phase alternatingcurrent circuit it through a transformer (as shown in Fig. 1) and the blower-cooled rectifier apparatus l3 with which is associated the fan 65 and driving motor 56; In addition to a disconnecting switch iil, the alternating current supply circuit M in Fig. 6 is provided with a switch means 65 having contacts lii in two or all of the phases of the alternating current line and an actuating winding il adapted to be connected to the direct current circuit ll through the normally closed contacts 35, d9 of a thermostatic switch unit 5@ and a two-prong plug 5i connected to one battery cable 413. The plug 5t coacts with sockets 52, 53 connected respectively to one side of circuit ll and to one side of winding ill, the

other cable plug 5 3 coacting with a socket 55' connected to the other side of circuit iii. The thermostatic switch unit 55 includes heater means 56 adapted during operation of the system to be continually energized from the alternating current circuit it. The direct current circuit Si is provided with a switch means 5i having contacts 58 adapted to be closed by an actuating winding 59 which is connected across a phase of alternating current circuit it through normally closed contacts 68, El of a thermostatic switch unit 82 having a heater means 63 continually energized during operation of the system from a phase of alternating current circuit ll. Motor it is also connected to one phase of alternating current circuit it through the contacts til, 65 of thermostatic switch unit 62. The thermostatic switch units 58 and 62 are arranged in the same manner as switch unit 2 a in Fig. l with reference to the air blast produced by fan l5.

In operation of the system shown in Fig. 6, switch means 35, 50, 5'17 and 62 being in their illustrated positions, upon insertion of plug 54 in socket 55 and of plug 511 in sockets 52, 53, switch is closed by battery current through contacts 48, 49 of thermostatic unit 50, assuming a residual charge in the battery sufdcient to actuate winding 4i. Uponclosing of the alternating current line switch 44, switch 57 is closed by current from alternating current circuit H and motor 16 is started. Heater elements 56 and 63 at the'same time begin immediately to heat, thereby tending to cause thermostatic units and 62 respectively to disconnect the alternating current circuit I l and the direct current circuit M from the rectifier system l3. Functioning of the thermostatic switch units 58 and 62 is, however, prevented by the action of the air blast produced by fan G5, in the same manner as above explained in connection with the operation of the system shown in Fig. 1. If plugs 5i and 54 are not in place in operative position to connect the storage battery to'direct current circuit ii, switch $5 is not closed and no current is suppliedfrom alternating current circuit ii to operate the rectifier apparatus it. If, after closing of alternating current line switch i ithe fan [5 does not start, the thermostatic devices heat up and cut ofif both the alternating current circuit M and the direct current circuit ll from the rectifier.

In the embodiment of the invention shown in Fig. 6, therefore, the rectifier apparatus is prevented from operating unless the battery is connected to the direct current circuit terminals; the rectifier apparatus is prevented from being connected to the battery in case the alternating current circuit fails; 5 and by means of the thermostatic units 58 and 632 both alternating current circuit it and direct current circuit 4! are opened in case of disablement of the fan E5 or stoppage of the air blast from any cause.

In Fig. 7 the system is similar in construction and mode of operation to the system above described in connection with Fig. 6 except that in Fig. 7 a three-phase motor M for driving the cooling fan i5 is provided adapted to be connected through leads G5, 66 and 5? to the alternating current circuit ii. If the battery load is not connected to direct current circuit li switch 65 remains open to disconnect the supply circuit it from the rectifier apparatus l3. Assuming, however, the battery loadto be properly connected and switch 45 thereby closed, upon closing of alternating current line switch it from all of the phases of circuit ii operates the motor it to rotate fan l5, and voltage across one phase of circuit it closes switch 571' to connect the rectifier apparatus 3 to the battery. Upon failure of the alternating current line i l the direct current circuit switch 5? opens to disconnect the battery from the'rectifier apparatus, and upon stoppage of the air blast the thermostatic units 58, 62 operate to open alterhating current circuit ii and direct current circuit ll, at the switches and 57.

In Fig. 8, showing'a battery charging system, the circuit arrangements are similar to those of the system shown in Fig. l for supplying a motion picture arc or similar load, in that in Fig. 8 the fan motor 55 and the heater 25 of the thermostatic unit 2 3 are supplied with current directly from the control circuit it through the switch ill, and an actuating winding 68 of a switch 69 in the alternating current supply circuit H is energized from the control circuit l8 through switch it and the contacts 22, 23 of the thermostatic unit. The system of Fig. 8, however, distinguishes from that of Fig. 1 by further including a switch 70 for the direct current circuit 4! having an actuating winding H which also is supplied with current from control circuit 18 through switch H and the contacts 22, 23 of thermostatic unit 24, and in addition a second switch 72 in the alternating current circuit H having an actuating winding 13 adapted to be supplied with direct current upon connection of a storage battery to the direct current circuit terminals 52, 53 and 55, in the manner explained in connection with Fig. 6.

current Ell;

by current from direct current circuit which v is connected td'the battery. Operating current is thereupon supplied to rectifier apparatus l3 from circuit ii. If, however, the battery is not connected to direct current circuit M the rectifier apparatus i3 cannot be operated on open circuit since switch l2 opens to disconnect the rectifier apparatus. from the supply circuit it. If, further, the air blast provided by fan l5 stops from any cause the rectifier apparatus cannot be operated, since the thermostatic unit 2 3 then operates to disconnect the actuating windings 68 and H from the control circuit it, thereby disconnecting supply circuit H from the rectifier apparatus at switch 69 and disconnecting direct current circuit M from the rectifier apparatus at switch iii.

In Fig. 9, the numeral i6 designates an elec-' tric transformer connected to an alternating current supply circuit 75 and adapted to be cooled by the fan l5 actuated. by the motor I5 which is supplied with current from the alternating current circuit. To protect the transformer from damage due to overheating, a thermostatic unit it, similar to thermostatic unit as of Fig. 1 for example, is provided having'normally closed contacts Ti, '88 in series with the actuating winding E9 of a switch between the alternating current line I5-andthe transformer. The thermostatic unit i6 includes a heater element 8! continually energized from the alter-- hating current circuit as long as the line switch 82 is closed. The actuating winding 79 of switch .80 is normally connected across the alternating current circuit 15 through the thermostatic unit 16. In operation, assuming line switch 82 closed,

as long as the air blast from the fan I! maintains heater M in cooled condition, switch 80 is held closed to connect the transformer to the supply circuit. But in' the event of stoppage of the air blast'from any cause, the thermostatic unit It functions to deenergize switch 80 and thereby disconnect the transformer from the supply circuit, in the same manner as above described for example in connection with the thermostatic unit 24 of Fig. l.

Instead of separate heater means for. the thermostatic switch units described in connection with the foregoing embodiments of my in.- vention, other means to cause functioning of the thermostatic'units may be employed, such for I example as the heating of a thermostatic switch,

inabove described, preferably of the type com- 'pensated for ambient temperature, provided that the protective means is controlled, in accordance with my invention, in response to the current of cooling medium.

It will be noted that the thermostatic switch means which I employ as protective devices for apparatus subject to damage from overheating are not so arranged as to operate only after the a rise of temperature in the apparatus has become objectionable or dangerous, as would be the case if the operation of the thermostatic unit 'depended on a direct riseof heat from the apparatus to be protected. In the prior protective arrangements when used, for example, with rectifiersit was necessary to waitguntil the copper oxide rectifier washers were actually heated and in damaged condition before the supply circuit wasopened. In accordance with my present invention, however, it is not necessary to wait,

before operating the thermostatic protective means, until the rectifier apparatus is hot, On

'the contrary the operation of the protective means is timed by the stoppage of the air blast from the fan, since the thermostatic unit-is.

continually energized by heating current but is cooled sufiiciently to prevent its functioning except, after a predetermined short period oftime,

in'the event that the air blast stops.

In those embodiments of my invention in which a load such as a storage battery or a motion picture are is supplied with direct current through a fanecooled copper oxide or other rectifier, the alternating current supply circuit has been illustrated as three-phase, and in the embodiment including a fan-cooled power transformer the supply circuit has been illustrated as single-phase. It will be understood, however, that the invention is not to be limited to apparatus including particular'typesof alternating current supply circuits, but that single-phase or any suitable polyphase supply circuits-may be utilized in the various embodiments of'the invention.

My invention has been described hreimin particular embodiments for purposes of illustration. It is to' be understood however'that the invention is susceptible of various changes and modifications and that by the appended claims I intend to cover any such modifications as fall within the. true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, 'an' apparatus characterized by the development of heat losses in operation, means to supply a current of cooling me-' dium to said apparatus to remove said losses, thermostatic means, heating means for said thermostatic means, and means to energize said heating means continuously during operation of. said apparatus, said thermostatic heating means being sufiiciently cooled by said current to main tain operation ofsaid apparatus during normal operation of the cooling medium supply means and said thermostatic heating means becoming sumciently heated upon disablement of said cooling medium supply means to stop said. development of heat losses. I

2. In combination, an apparatus characterized by the development of heat losses in operation, means to supply a current of cooling medium to said apparatus to remove said. losses, thermostatic means, heater means for said thermostatic means, means to energize said heater means continuously during operation of said apparatus, means including said cooling medium supply means to cool said heater means and thereby to maintain operation of said apparatus during normal operation of said cooling medium supply means, 'and means operative upon disablement of said cooling medium supply means and upon the consequent rise in temperature of said heater means to stop said develop- 'ment of heat losses.

ergized heater means mounted in said air blast, said heater means being adapted to be cooled sufiiciently during normal operation of the air supply means to cause said thermostatic switch means to maintain operation of said apparatus, said heater means being adapted to become heated sufliciently upon disablement of the air supply means to operate said thermostatic switch means to stop operation of said apparatus.

4. In combination, a power rectifier apparatus including a rectifier having a blower means to prevent rise of temperature of said rectifier above a predetermined limit, a thermostatic switch means for controlling the operation of said rectifier, means for supplying heat continuously to said switch means during operation of said apparatus, said switch means being adapted to be cooled by the blower means, said switch means being so arranged as to cause operation of said rectifier during normal operation of the blower means and to stop operation of said rectifier upon disablement of the blower means.

5. In combination, a rectifier apparatus including a rectifier and a cooling fan associated therewith to permit relatively high current flow through said rectifier without a temperature rise therein above a predetermined limit, a thermostatic switch means compensated for ambient temperature variations for controlling the operation of said rectifier, means for supplying heat continuously to, said switch means during operation of said apparatus, the thermostatic switch means being so mounted with respect to the fan as to be cooled by air therefrom and being so arranged that said current is caused to fiow in said rectifier during'normal operation of said fan and that said current flow is stopped upon stoppage of said fan.

6. In an electric apparatus for supplying power to a direct current circuit from an alternating current circuit, said apparatus comprising a rectifier and a blower to supply cooling air thereto, a switch means between said rectifier and said alternating current circuit, a control circuit, a motor supplied with current from said control circuit to actuate said blower, a thermostatic device to cause current from said control circuit to operate said switch means, means for supplying heat continuously to said thermostatic device during operation of said apparatus, said thermostatic device being adapted to be cooled by cooling air from said blower and being so arranged that said switch means is closed to connect said rectifier to said alternating current circuit during normal fiow of cooling air from the blower and that said switch means is opened upon stoppage oi the blower cooling air.

'7. In an electric apparatus for supplying power to a direct current load circuit from an alternating current circuit, said apparatus comprising a rectifier and a blower to supply cooling air thereto, a pair of terminals for the direct current circuit, a switch means between the rectifier and the alternating current circuit, a second switch means between the rectifier and at least one of said terminals, a motor supplied with current from the alternating current circuit to actuate said blower, and two thermostatic devices arranged respectively to control the operation of said first-named and said second-named I switch means, said thermostatic devices being adapted to be-ccoled by cooling air from said blower and being-so arranged that both of said switch means are closed to connect the rectifier to the alternating current circuit and to said direct current circuit terminals during normal flow of cooling air from the blower and that both of said switch means are opened upon stoppage of the cooling air.

8. In an electric apparatus for supplying power to a direct current load circuit from an alternating current circuit, said apparatus comprising a rectifier and a blower to supply cooling air thereto, a pair of terminals for said direct current load circuit, a switch means between the rectifier and the alternating current circuit adapted to be operated by current from the direct current circuit, means associated with said terminals to prevent flow of operating current for said switch means until the load circuit is connected to said terminals, a second switch means between therectifier and at least one of said terminals, a motor supplied with current from the alternating current circuit to actuate said blower, and two thermostatic devices arranged respectively to control the operation of said first-named and said second-named switch means and each having a heater element adapted to be cooled by cooling air from the blower, said thermostatic devices being so arranged that both of said switch means are closed to connect the rectifier to the alternating current circuit and to said direct current circuit terminals during normal flow of cooling air from the blower. and that both of said switch means are opened upon stoppage of the cooling air.

9. In a rectifying apparatus for charging a storage battery from an alternating current circuit, said apparatus comprising a rectifier and a blower to supply cooling air thereto, charging terminals adapted to be connected to the battery, a switch means in series between the rectifier and the alternating current circuit, circuit connections between said terminals and said switch means to supply operating current to said switch means, means associated with said terminals to prevent fiow of operating current for said switch means until the battery is connected to said terminals, a second switch means between the rectifier and at least one of the terminals, a motor supplied with current from the alternating current circuit to actuate the blower, and two thermostatic devices arranged respectively to control the operation of said first-named and said second-named switch means and each having a heater element adapted to be cooled by cooling air from the blower, said thermostatic devices being so arranged that both of said switch means are closed to connect the rectifier to the alternating current circuit and to said direct current circuit terminals during normal flow of cooling to be operated by current from the direct cur rent load circuit, means associated with said t e 1 minals to prevent flow of operating current for said one of the switch means until the direct current load circuit is connected to said terminals, a control circuit, a motor supplied with current from said control circuit to actuate Said blower, and a thermostatic device arranged to control the flow of operating current from the control circuit to the other of said switch means, said device having a heater means continually supplied with current from the con- .trol; circuit and adapted't'o be cooled by said "cooling air, said thermostatic device being so 1 arranged that said other of said switch means is closed to connect the rectifier to the alternating current circuit during normal fiow of said cool ing air from said blower and that said other of the switch means is opened upon stoppage of the cooling air.

11. In a rectifying apparatus for charging a p storage battery from an alternating current cir- 15 saidswitch/means to supply operating current theretameans associated with said terminals to prevent flow of operating current to one of said switch means until the battery is connected to said terminals, a control circuit, a motor supplied with current from said control circuit to actuatesaid blower, and a thermostatic device;

arranged to control the flow of operating current from the control circuit to the other 01 said switch means, said device having a heater means continually supplied with current from the control circuit and adapted'to be cooled by cooling air from said blower, said thermostatic device being so arranged that said other of said switch means. is'closed to connect the rectifier to the alternating current circuit during normal flow of cooling'air from said blower and that said' other of the switch means is opened upon stoppage of the cooling air.

, EGAR A. HAR'I'Y, 

